Making an outrigger boat kit available for $35 shipped, need input!

[slowsl]

Is it necessary to detongue the props?

[Fluid]

No, not necessary, they run well as designed. Detonguing can give a bit more speed, but I'd wait until you have more prop experience before detonguing.


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[Peter A]

I have a predator (retired) that with a 3650 3300kv hobbyking motor. On 3s 4000-4500 mah packs, x632 prop and a T-90 esc would do around the 50mph mark. With a x437/3 it was a rocket but became unstable at high speed.

[slowsl]

I have a predator (retired) that with a 3650 3300kv hobbyking motor. On 3s 4000-4500 mah packs, x632 prop and a T-90 esc would do around the 50mph mark. With a x437/3 it was a rocket but became unstable at high speed.

Awesome, that is around the rpm mine will be turning. I've only got a 3300mah battery to save on weight. Was it the boats design or the 3-blade that would make it unstable at high speed? What were the characteristics at that speed that made it unstable, and how could the design be improve to make it more stable?

[Fluid]

The Predator was designed ten years ago for 6-8 NiMH cells and a small brushed motor. It has plenty of lift in the sponsons to get the 'heavy' boat up and runing with its limited power. Double the power with LiPos and a good BL motor and it has too much lift, hense the unstable running. Outrigger sponson aoa has to be suited for the weight/speed envelope of the boat, otherwise it will not perform well. For example, the modern JAE 21FE rigger has a pretty wide performance envelope, from the 50s well into the 70s even with the same weight.

[Fluid]

The Predator was designed ten years ago for 6-8 NiMH cells and a small brushed motor. It has plenty of lift in the sponsons to get the 'heavy' boat up and runing with its limited power. Double the power with LiPos and a good BL motor and it has too much lift, hense the unstable running. It is pretty small for running on anything but smooth water at high speed.

Outrigger sponson aoa has to be suited for the weight/speed envelope of the boat, otherwise it will not perform well. For example, the modern JAE 21FE rigger has a pretty wide performance envelope, from the 50s well into the 70s even with the same weight.


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[slowsl]

The Predator was designed ten years ago for 6-8 NiMH cells and a small brushed motor. It has plenty of lift in the sponsons to get the 'heavy' boat up and runing with its limited power. Double the power with LiPos and a good BL motor and it has too much lift, hense the unstable running. It is pretty small for running on anything but smooth water at high speed.

Outrigger sponson aoa has to be suited for the weight/speed envelope of the boat, otherwise it will not perform well. For example, the modern JAE 21FE rigger has a pretty wide performance envelope, from the 50s well into the 70s even with the same weight.


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I see. Bear with me on this, as I know nothing about boat design, but just some thoughts....
Would narrowing the sponsons, say 25-30% have a stabilizing effect on plane? I'm guessing less surface area on the water would likely make the sponsons ride a little more wet, giving it a bit more "traction". Or what about, say looking straight at a sponson from the front, instead of making it flat-bottomed, have it slightly concave upward. This would put the outter edges down into the water a little more than the center. This may act as a stabilizer for the front at least. Is the front or the back of the boat the problem when you get to those speeds? I would almost think a super thin, short, long (1/4" into the water, and about 1.5" long) stabilizer fin attached to the side of the rear sponson may help keep the rear end from sliding out at speed. I know this would of course create more drag, but I wouldn't think it would be much, with sharpened thin material used. Am I way out in left field here? If my boat becomes unstable, I'm going to test different things until I get it right.

[Fluid]

Getting the sponsons just right takes testing. Sure, narrowing the sponsons reduces lift, but also reduces buoyancy when the boat is stopped or partially flodded. You don't want the rigger to sink if one sponson gets knocked off and the tub floods! It all becomes a balancing act of width and aoa.

You definately want a flat bottomed sponson, not curved. The rudder keeps the transom from sliding, another fin just adds drag with no benefit. At higher speeds it is the front sponsons which usually cause problems, the rear end can get bouncy if the wrong prop or prop depth/angle is used.

While a rigger looks simple - just a tub, sponsons and sticks - designing a good one takes time. There are a number of riggers on the market, they sell because they perform better than 'regular' hydroplanes and 'look' fast. The better ones took a long time and many different designs to develop, and their superior performance shows. The highly successful JAE riggers took years of development with multiple experts lending a hand in design and testing. Too bad they are so ugly! (I love driving mine BTW).

I've designed and built a number of riggers in the past thirty years and frankly the oval designs didn't work out as well as I wanted. I had much more luck with SAW riggers, they only had to go straight and had a pretty narrow speed envelope. It isn't easy unless you get lucky. I wish you luck, and I bet you can come up with a good-running rigger.


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[Peter A]

Awesome, that is around the rpm mine will be turning. I've only got a 3300mah battery to save on weight. Was it the boats design or the 3-blade that would make it unstable at high speed? What were the characteristics at that speed that made it unstable, and how could the design be improve to make it more stable?

I put narrower ride pads on the sponsons but it's size has limitations at speed. Put it this way, a nitro .45 sgx eagle took three laps to catch me before I spilled on lap four, that was with the 437/3. Too small a boat when the water starts to ripple in a race. The solution was to build a bigger version, that was run with 4s setups and is currently shelved until I can afford a 6s setup for it.

[slowsl]

Got it back on the water this morning. It was a bit windy, the water was pretty choppy, but I just needed to test out the new radio/receiver. It went great, other than my dog freaking out and jumping in the water to go after it. The radio had very good range, never lost contact. I could only manage about 30mph before it bounced violently from the waves, but so far so good. I can't wait to open her up on some smoothe water. Hopefully tomorrow will be better.
Here are some closeup pics, if anyone can spot anything that might be a problem, please let me know.

[slowsl]

As long as everything is progressing, I will start building version 2 and testing soon.
Version two plans are to enlarge the tub a bit, in order to fit the larger setups. Mine seems to fit and have a little room to adjust COG, but it's very tight. Just need 1/4" in both directions. There will be quite a few changes to make easier access to the motor/shaft collar, etc. The prop right now sits about 2.5" out back from the tub. I will be redesigning the main sponsons for a slightly smaller wet surface area, and also moving them forward an inch or two, and placing them out another inch or two for greater stability, will see how this turns out.

[siberianhusky]

Why not just build a JAE .12 rigger from the free plans, I have a nitro one and am considering an electric. Great running well tested hull for modern power.

[NativePaul]

I have a JAE.12 lightly modded for FE (bulkhead and boom placement) and the thing is a tank, it needs either much thinner ply or a much taller tub to fit more power inside IMO.

[slowsl]

Yeah, I didn't spend a lot of time researching the different models out there. I just needed something to start with and the Predator seemed to be about the size I was looking to start with. I've learned a lot from crawling the internet, and a big thanks to all the people who helped my with my newb questions. Here is the first real test of the boat, turned out good I think.

[slowsl]

UPDATE!!!
I've made huge leaps over the last couple weeks. The revised version was thrown in the water today in some pretty rough water with the same waves that are present in the posted video. This time, the boat cut right through the waves. It stuck pretty good to the water all around, and all of the geometry was just roughly set by eye. I think this version is the one I will be making soon. It handles great for its small size. I figured out a great way to make adjustable, removable main sponsons, which you can see in the pics. This will be available as an extra kit when I figure it out. I kind of forgot about the turn fin location when I made these, so I will have to rethink that. I will also post a preview pic of the larger boat I'm designing, we will see how that turns out.
So I was able to get out there the other day with some decent water. I wanted to benchmark the 3 props I have balanced & sharpened with my bushnell velocity radar gun. I think I need to thin the props, I get quite a bit of prop walk, but not so much that it's out of control. I managed about 5 straight speed tests on each prop. I started with a x442, then went to a 1740, then to a 1938. After the two larger props, the motor was very hot, I'm sure the electronics would burn out after a while.
x442 - 48mph
1740 - 42mph
1938 - 50mph
I'm going to order a 2137/3 , v937/3, 2337, and 2035 and see what I get with those, should be smaller diameter and higher pitch according to the octura prop chart. I think the 3 blades may be too much prop to run through an entire battery though, but I guess there is only one way to find out.

The boat now handles extremely well around an oval, and hangs tight around the corners at full speed. I'll post up a video next time I'm out, I'm very happy with the way the boat is coming together.

So next I will be testing different sponson angles for top speed and handling and finding the optimum angles. I will try out the new props, and try a couple different turn fins. I'm going to put a bend in them to try to keep the side down around the corners. I imagine it's losing a bit of speed from the left sponson digging deep in the corners. I think it's balanced nicely, balance point being about a 1/2" behind the turn fin. I think I've got the strut angle set where it needs to be, the shaft is about 1/8" above plane, and angled slightly down. Other than getting into propwork, what else can be done in order to improve the boat?
-Mike